Improved method of bonding filter elements



y 1962 H. E. JACKSON 3,042,571

IMPROVED METHOD OF BONDING FILTER ELEMENTS Filed Sept. 5, 195a 2Sheets-Sheet 1 '4 jar,

1 ORA/E) y 1962 H. E. JACKSON 3,042,571

IMPROVED METHOD OF BONDING FILTER ELEMENTS Filed Sept. 5, 1958 2Sheets-Sheet 2 /NVEN TOR ATT E) States atent 3,042,571 IMPRG'VED METHODOF BONDING FILTER ELEMENTS Harold Ernest Jackson, Plyrnpton St. Maurice,England, assignor to Tecalernit Limited, Brentford, England Filed Sept.5, BS3, Ser. No. 759,167 13 Claims. 3], 156-191) This invention relatesto the construction of filter elements and it is more particularlyconcerned with the can struction of elements of the type in which thefilter element consists of one or more sheets of filter material whichis or are pleated, folded or otherwise formed into an annular or otherrequired shape and one or more of the edges of which is or are securedto at least one end cap or other member, which holds the filter material1n position and prevents the flow of fluid round, instead of through,it. Such filters include, inter alia, those of the star type, in which asheet of filter material is pleated and secured in the form of anannular star (in crosssection) between a pair of .annular end caps toform the filter element, and those comprising one or more cylinders or ahelix of filter material, which is or are secured between a similar pairof end caps to form the filter element.

Another form of filter, to which the invention is applicable, is one inwhich a strip of filter material is pleated along transverse fold linesand is then arranged in a fanlike manner to form an annular element of amore or less disc-like form, in which the pleats radiate from thecentre. in this latter form of filter element, the edges of the filtermaterial may be secured to an inner tube and also to an outer sealingband, which parts may be made of paper or other suitable material, toretain the shape of the element and to control the passage of the fluidthrough the filter material, from one side of the filter element to theother.

When constructing filter elements in which the filter material, inpleated or other form, is fitted between a pair of end caps, one priormethod which has been employed for securing the edges of the material tothe end caps consists in applying a liquid adhesive or cement to theinner surface of each end cap, after which the ends of the filtermaterial are pressed against the film or layer of adhesive or cement,which secures the parts together.

Such known methods for securing the end caps of filter elements sufferfrom various drawbacks and difllculties, particularly when it isnecessary to ensure the provision of an effective leak-proof bond underconditions of large scale production. Under such conditions, it isnormally necessary for mass production, in order to provide a margin ofsafety, to utilise a larger quantity of adhesive or cement on the innerfaces of the end caps than is strictly necessary to provide an adequatebond which is uneconomical and the excess flows onto the surfaces of thefilter material, thus reducing its filter area and the effectiveness ofthe latter. Another difiiculty is due to the risk of air being entrainedwhen the filter material is being embedded in the liquid adhesive orcement, with the resultant possibility that air bubbles formed may causethe bond to leak. Furthermore, it has been proposed to apply lengths ofpre-formed tapes at and embracing around the edges of a strip of filtermaterial, these tapes being composed of a solidified cellulose orresinous substance which may be dissolved or softened by a solvent tocause them to be adhesive. This requires the extra-step or steps ofmaking the sheet material of such substances, of cutting the sheet intotapes of required width to embrace around the edges of the filtermaterial, of rolling these tapes onto the edges of the filter material;and the width of such tapes provides a wasteful excess of non-usefuladhesive substance with its attendant drawback of fouling the filtermaterial when so dissolved to render it adhesive to the end-caps of thefilter element. i

It is accordingly one of the principal objects of the present inventionto provide a new method for manufacturing filter elements in which,broadly, a soft adhesive substance is applied directly as a small headto and along the edges of the filter material and is thereafter bondedto end caps or other members devoid of an adhesive, thereby overcomingthe above mentioned drawbacks and difficulties and providing the mosteconomical, elficient and reliable manner of assembling a unitary filterelement with a minimum of adhesive by having no adhesive on the end-capsor other surfaces except only at the points of bonded contact of thefilter material therewith.

Another obiect of the present invention is, more specifically, toprovide a method of bonding a filtering material in sheet form to anadjoining member in the construction of a filter element unit, wherein abead of an adhesive substance is first formed along an edge or afold-line of the filter material or medium by applying said substancealong said edge or fold-line while the substance is in a liquid,semi-liquid or plastic state, after which the substance is allowed toharden so that the filter material can be handled, folded or otherwisemanipulated into form in the mass production of said filter elementunits; and wherein the said formed filter material is then attached toan adjoining member or members (such as end caps or inner and outerbands or tubes), having no adhesive substance thereon, by pressing saidhead against the said adjoining member or members while causing asoftening of the bead followed by a rehardening of the latter whichcauses the filter material to adhere to said member or members.

A further object of the invention is to provide a method of forming afilter element comprising at least one band or strip of a filtermaterial which is rolled or folded into a helical, annular or zig-zagform and one edge at least of which is secured to an end cap or othermember to support the filter material and prevent the flow of fluidbetween it and the said member, wherein the edge of the strip is securedto the said member by the above method.

The invention will now be more fully described, by way of example, withreference to the accompanying drawings, in which:

FIGURE 1 is a plan view, partly cut-away, showing a length or strip of afilter material which may be used in the construction of a filterelement according to the invention;

FIGURE 2 is a section, taken through the filter material on the line AAof FIGURE 1;

FIGURE 3 is a general view showing one form of filter elementexemplifying the invention, before its final assembly; 7

FIGURE 4 is a view similar to FIGURE 3 but showing a modified form offilter element;

FIGURE 5 is a plan view showing another form of filter element which maybe constructed in accordance with the invention;

FIGURE 6 is a partly cut away side view of the element shown in FIGURE5; and

FIGURE 7 is a section taken on the line lB-B of FIGURE 5 Referring firstto FIGURES 1, 2 and 3, the filter element shown is constructed from alength or strip of filter paper or other filtering medium 1. The twolongitudinal side edges of this strip are formed with heads 2 made of asuitable adhesive or bonding substance. This substance may be one whichcan be applied to the edges of the strip in a liquid, semi-liquid orplastic state, after which it can be allowed or caused to harden. Thus,the

adhesive substance may be one which can be melted or softened by heat,such as nylon or polythene or another thermoplastic synthetic resinhaving the required properties, or alternatively an adhesive substancemay be used which is rendered liquid or plastic by the inclusion in itof a solvent. Examples of suitable adhesives or bonding agents, whichmay be inorganic and/or organic of natural or synthetic origin, areknown and sold under the registered trademarks Bostik and Pliobond andinclude various synthetic resins which are rendered liquid orsemi-liquid by the inclusion in them of suitable volatile solvents. Itis also possible to make use of natural or synthetic rubber latex and ofsuitable adhesives having a starch base.

The adhesive or bonding substance may be applied to the edges of thestrip 1 to form the beads 2 in any suitable manner. For example, theedges of the strip 1 may be dipped in the adhesive or bonding substancein liquid form or said edges may be passed over a roller or othersuitable member coated with the substance. Alternatively, the adhesiveor bonding substance may be applied by extrusion, as in a continuouscohesive stream-mass or in a nebulized spray.

Whichever method of application is used, the adhesive or bondingsubstance is then caused or allowed to harden on the strip 1 to form thebeads 2, which facilitates the subsequent handling and manipulation ofthe strip 1 in the construction of the filter element resulting in theproduction of a tubular band of filter material having continuous beadsof a hardened adhesive or bonding substance in solid form along its endedges and which will not interfere with the handling and manipulation ofthe band before and during the assembly of the filter ele ment.

To form the filter element shown in FIGURE 3, the strip 1 of filtermaterial with the beads 2 along its side edges is pleated alongsubstantially parallel and spaced fold-lines transverse to its lengthand is folded to form a pleated annulus, as shown, in FIGURE 3, the twoends of the strip being secured together in any suitable way to form atubular band using, if desired, the same adhesive or bonding substanceas has been used to form the beads 2. Such a substance may, in fact, beinitially applied to the ends of the strip 1 to form beads on the lattersimilar to the beads 2 on its side edges. The strip I of filtermaterial, having been so formed and the adhesive 2 thereon being dry andsolid, may be, and sometimes is, stored for subsequent assembling into acompleted filter element.

Thereafter to complete the filter element, holding and fluid directingmeans in the form of a pair of annular end caps 3, which are shown ashaving inner and outer lips or rims 4 and 5, are applied to the ends,respectively, of the pleated tubular filter material or member. Thesecaps may be formed of any suitable material, including sheet metal(which may be pressed to shape), cardboard (which may be pressed ormoulded to shape) and synthetic plastics (which may be moulded toshape).

To assemble the filter element into a unitary structure, the tubularpleated filter material 1 with its bead 2 is fitted between the two endcaps 3 and pressure is applied to the latter. If a thermoplaticsubstance is used for the heads 2, suificient heat is applied to softenthis substance and to cause it to adhere to the caps 3. Alternatively, asolvent may be used to soften the adhesive.

After cooling or the evaporation of the solvent to cause the adhesivesubstance to harden, the pressure can be released and the end caps 3will remain firmly attached to the filter material. Since the heads 2formed along the edges were continuous, there is no likelihood of anygaps occurring in the bonding of the end caps, which might allow leakageof the fluid being filtered round the edges of the filter material.

FIGURE 4 shows another form of a filter element, in which a strip 21 offilter material having beads 22 (similar to the heads 2), instead ofbeing pleated, is wound t into the form of a helix. The inner and outerends of the band are secured to the adjacent turns or convolutions ofthe helix in order to form inner and outer cylinders of filter material.

The helix of filter material 21, shown in FIGURE 4, is fitted betweenand is secured to a pair of end caps 23 (similar to the caps 3) by anyof the methods which have been described with reference to FIGURE 1.

Similar methods may also be employed, if a band. or hands of filtermaterial is or are used which is or are simply formed into one or moreconcentric cylinders by connecting the ends of the or each band togetherbut provided with the heads 2 or 22 of the aforesaid bonding material.

Any of the filters which have been described can also include otherholding and fluid directing means in the form of an inner tube 7 (FIG.3) made of perforated metal or of any other suitable material throughwhich the fluid being filtered can pass and such a tube may be securedto the end caps 3 or 23 in the same way as the filter element 1 or 21 ifbeads of the adhesive or bonding substance are first formed round theedges of the tube at the ends of the latter.

Furthermore, in the filters which have been described, a metal mesh orother suitable support may be provided for the filter material and,again, a similar method may be employed for securing such a support tothe end caps by means of beads of adhesive formed along the edges of thematerial used for the support.

FIGURES 5 to 7 show another form of filter element of the general kindwhich comprises a strip of filter material 31, similar to that shown inFIGURES l and 2, having edge beads 32 of adhesive, similar to the beads2 or 22, which is first pleated along spaced transverse fold lines andits ends are secured together. This forms a pleated tubular filterelement which appears somewhat similar to the element 1 shown in FIGURE3. In the present case, however, in order to form the filter element 31,one end of the thus formed, pleated tube-form is opened and/or spreadoutwardly so that the material takes the form of a pleated amiular discwith the fold lines of the pleats at the other or inner end groupedcloser together and radiating outwardly from the centre in the manner ofa fan. In this form of a filter element, a holding and fluid directingmeans may be employed in the form of an impervious central tube 33 andan outer surrounding impervious band, sleeve or ring 35. The centraltube 33, which may be made of paper, card, metal or suitable material,is fitted inside the annulus and is secured to the inner beaded edge 32of the pleated filter material by the use of heat or a solvent, whichsoftens the adhesive head 32 on that edge. The tube 33 may be formedwith a flange at one end, if desired, or a separate flanged sealing ring34 may be inserted, being secured by any suitable adhesive which may ormay not be the same as that used for the beads 32. The band 35 surroundsfilter element and contacts the adhesive bearing outer edges thereof.This band, sleeve or ring 35 may consist of a ring of an elasticmaterial, such as natural or synthetic rubber; and, alternatively, itmay be provided by a strip of paper or other material, which may not beelastic and which is fitted or wound round the filter elements.

Whichever method is employed, if the outer edge of the pleated filtermaterial 31 has been provided with a bead of an adhesive substance 32,similar to the inner head 32, this may be used to secure the outer ringor band 35 in position by one of the methods which has been described,this preferably being done at the same time as the attachment of theinner head to the central tube.

Although the present invention has been more particularly described asapplied to the attachment of the edges of the filter material to endcaps or other members, the same principle may be employed in cases inwhich it may be desired to secure the fold lines of a folded or pleatedfilter material to an adjacent part, such as the inner fold lines 6 ofthe filter material 1 of FIGURE 3, to and along which fold lines 6 abead 2a of said thermoplastic or solvent-plastic adhesive in liquid formis deposited, in order that an inner central tube 7 may be securedthereto. The necessary beads 2a of the adhesive or bonding substance areapplied to the folds 6, after the forming of the pleats, by any suitableone of the methods which have been described.

Having thus described the invention and the manner in which the same isto be performed and constructed, it is to be understood that changes andmodifications may be made in detail construction of parts and inspecific arrangement of parts shown and described and that such changesas fall'within the scope of the appended claims are within the purviewof the present invention and contemplated thereby.

That which is claimed, as new and to be secured by Letters Patent, is:

1. A method of bonding a filter material in sheet form to an adjoiningholding means in the construction of a filter element unit, which methodcomprises first forming a bead of an adhesive substance on at least oneend edge of a filter sheet by depositing said adhesive substance alongsaid edge, while the adhesive is in a soft state and allowing said beadto dry and harden so that the filter sheet may be handled andmanipulated into the form of a filtering element; then, shaping saidsheet into a circular form; then applying a holding means devoid ofadhesive thereon to the bead of adhesive of said edge of said filtersheet and subjecting said bead to a softening step and, while sosoftened, pressing said head against said adjoining holding means; andthen subjecting said bead to a rehardening step to cause the edges ofthe filter material to be bonded to said means.

2. A method as claimed in claim 1, wherein the adhesive is athermoplastic substance which is subsequently softened by heat to causeit to adhere to the said holding means.

3. A method as claimed in claim 1, wherein the adhesive contains asolvent the evaporation of which causes the adhesive to harden afterbeing applied to the filter material to form the bead; and wherein theadhesive is subsequently softened by the application of a solventthereto to cause it to adhere to the said holding means.

4. A method as set forth in claim 1, wherein the bead is formed bydipping the edge or fold line of the filter sheet in a liquid adhesivesubstance.

5. A method as set forth in claim 1, wherein the adhesive substance isapplied to the filter material by moving said edge thereof over a membercarrying the adhesive substance in liquid form.

6. A method as set forth in claim 1, "wherein the bead is formed byextruding said adhesive in a continuous mass onto said edge of thefilter material.

7. A method as claimed in claim, 1, wherein the adhesive substance issprayed onto said edge of the filter material to form said bead thereon.

8. A method of forming a filter element as set forth in claim 1, furthercharacterized by the shaping step comprising the coiling of said sheetof filter material into a helical-form with spaced convolutions; and bythe holding means being an annular end-cap and the bonding stepincluding the capping of the ends of the helicalform with annular capspressed against said beads, whereby the end edges of said helical-formare secured to said end-caps.

9. A method of forming a filter element as set forth in claim 1, furthercharacterized by folding said sheet of filter material to form amultiplicity of substantially adjacent pleats and applying a head of asoft adhesive substance continuously along the outwardly projectingedges of said folds on one surface of said sheet and allowing saidadhesive to harden; and by said shaping step includ ing the bringing ofsaid sheet into a cylindrical-annular form with the pleats extendingaxially of said form and with the adhesive-bearing fold-edges extendinginwardly of said form; and by said holding means being annular end-capsfor the ends of said form and a tube inserted in the center opening ofsaid form; and by the bonding step including the capping of the ends ofthe annular form with a pair of end-caps pressed against said softenedbeads of adhesive substance on opposite ends of said form and thesoftened adhesive on the fold-edges of the pleats being pressed againstsaid tube.

10. A method of fabricating a filter element unit which comprisesproviding an elongated sheet of filtering material with a continuoushead of hardened unpolymerized adhesive substance along each of its twoopposite side edges; then pleating said sheet along substantiallyparallel and spaced lines extending transversely of the sheet betweenthe beads on its side edges; then applying a bead of said adhesive in asoftened condition to and along each outer fold-line on one face of saidsheet and allowing the said beads to harden; then shaping said pleatedsheet into a cylindrical-annulus with its meeting edges: securedtogether and with said adhesive bearing fold-lines projecting inwardlyof said cylindrical-annulus and the beads on said side edges being atthe ends of said pleated cylindrical-annulus; inserting a tubular membercentrally into said pleated cylindrical-annulus in opposing relation tothe adhesive substance on the inner fold-lines of said pleats; applyingannular end caps to the ends of said pleated cylindrical-annulus; andthen subjecting said adhesive material on the ends of said pleatedcylindricalannulus and on the inner fold-lines of said pleats to asoftening step while pressing said end caps against the beads on theends of said pleated cylindrical-annulus and pressing saidadhesive-coated fold-lines of the pleats against said inserted centraltube; and then allowing said adhesive material to reharden, wherebysecuring said parts together with a continuous bond in a filter elementunit.

11. A method of fabricating a filter element unit which comprisesproviding an elongated sheet of filtering material and applying acontinuous bead of an adhesive substance along at least one of itslongitudinal edges while the adhesive is in a soft state and allowingsaid beads to harden; then pleating said sheet transversely of itslength; then shaping said pleated sheet into an annular disc-like formwith the longitudinal length of said pleats radiating outwardly from itscenter and its meeting ends secured together and with said bead ofadhesive at its inner diameter; inserting a tubular member into thecenter opening of said annular disc-like form in contact with the beadof adhesive substance at its inner edge; and subjecting said bead ofadhesive material to a softening step while pressing said softenedadhesive head against said inserted central tube; and then allowing saidadhesive material to reharden to secure the parts together with acontinuous bond.

12. A method of fabricating a filter element unit which comprisesproviding an elongated sheet of filtering material and applying acontinuous head of an adhesive substance along each of its twolongitudinal edges While the adhesive is in a fiowable state andallowing said beads to harden; then pleating said sheet transversely ofits length; then shaping said pleated sheet into an annular disc-likeform with the longitudinal length of its said pleats radiating outwardlyfrom its center and. with its meeting end edges secured together;inserting a tubular member into the center opening of said annulardisc-like form in contact with the head of adhesive substance at theinner edge of said annular disc-like form and surrounding the outer edgeof said pleated disc-like form with an enclosing band-strip; andsubjecting said beads of adhesive material on the edges of said pleateddisc-like form to a softening step While pressing said beads againstsaid tubular member and said enclosing band-strip; and then allowingsaid adhesive material to reharden to secure the parts together with acontinuous bond.

13. A method of fabricating a filter element unit which includespleating an elongated sheet of filtering material transversely of itslength; applying a bead of a soft adhesive substance continuously alongthe outer folded edges of the pleats projecting from one surface of saidsheet and allowing said adhesive to harden; then bringing and securingtogether the opposite end edges of said pleated sheet to form acylindrical-annulus with said adhesive bearing fold-lines of the pleatsprojecting inwardly of said annulus; then inserting a tubular membereentrally into said pleated annulus in opposing relation to saidadhesive bearing fold-lines; then subjecting said adhesive material to asoftening step While pressing said adhesive bearing fold-lina againstsaid inserted central tube; and then allowing said adhesive material toreharden, whereby securing said parts together with a continuous bond.

or References Qited in the file of this patent UNITED STATES PATENTS

1. A METHOD OF BONDING A FILTER MATERIAL IN SHEET FORM TO AN ADJOININGHOLDING MEANS IN THE CONSTRUCTION OF A FILTER ELEMENT UNIT, WHICH METHODCOMPRISES FIRST FORMING A BEAD OF AN ADHESIVE SUBSTANCE ON AT LEAST ONEEND EDGE OF A FILTER SHEET BY DEPOSITING SAID ADHESIVE SUBSTANCE ALONGSAID EDGE, WHILE THE ADHESIVE IS IN A SOFT STATE AND ALLOWING SAID BEADTO DRY AND HARDEN SO THAT THE FILTER SHEET MAY BE HANDLED ANDMANIPULATED INTO THE FORM OF A FILTERING ELEMENT; THEN SHAPING SAIDSHEET INTO A CIRCULAR FORM; THEN APPLYING A HOLDING MEANS DEVOID OFADHESIVE THEREON TO THE BEAD OF ADHESIVE OF SAID EDGE OF SAID FILTERSHEET AND SUBJECTING SAID BEAD TO A SOFTENING STEP AND, WHILE SOSOFTENED, PRESSING SAID BEAD AGAINST SAID ADJOINING HOLDING MEANS; ANDTHEN SUBJECTING SAID BEAD TO A REHARDENING STEP THE EDGES OF THE FOLTERMATERIAL TO BE BONDED TO SAID MEANS.